A federal judge refused yesterday to prevent the head of President Clinton's security detail from being forced to testify about Monica S. Lewinsky this morning, leaving administration lawyers scrambling overnight for a last-minute reprieve, according to sources close to the case.

During a hastily convened, closed-door hearing in her chambers, Chief U.S. District Judge Norma Holloway Johnson harshly chastised the Secret Service for continuing to fight independent counsel Kenneth W. Starr's efforts to obtain testimony, the sources said, and she would not grant the agency's request to put the latest subpoenas on hold.

In an unusual move, Johnson issued no written ruling turning down the motion, but Justice Department lawyers representing the Secret Service filed an emergency motion asking the federal appeals court to intervene last night anyway, according to a source. If unsuccessful there, the department planned to seek help from Chief Justice William H. Rehnquist.

The high-wire confrontation set up a possible showdown for this morning. With Special Agent Larry L. Cockell and other Secret Service officers ordered to appear at the federal courthouse in Washington at 9:15 a.m., the Justice Department had just hours to persuade a higher court to step in before Starr brings the witnesses into the grand jury. According to people familiar with the situation, Cockell may be advised not to show up if the subpoena is not blocked in time.

The sudden escalation of Starr's six-month campaign to secure Secret Service testimony about Clinton's relationship with Lewinsky converted what had been a polite debate among lawyers about legal privileges into a politically charged fistfight in which neither side appeared willing to back down.

Until this week, Starr had been content to wait until the legal process played itself out, but he apparently grew tired of delays by the administration after winning support from the appeals court last week and decided to force the issue. In addition to Cockell, the plainclothes agent who has overseen the presidential protective division since February, Starr on Tuesday subpoenaed seven uniformed officers, officials said yesterday, one more than previously reported.

"We will use all legal and prosecutive means to get this information as fast as we can," said Starr spokesman Charles G. Bakaly III.

The White House reacted swiftly and fiercely, condemning the move as the action of "an overzealous prosecutor" trying to force the president's protectors to "betray that trust," as press secretary Michael McCurry put it. Clinton's private attorneys vowed a vigorous new court battle if Cockell is asked about the president's conversations with them.

"These are tactics that are certainly questionable and that's a mild way of saying it," McCurry said.

In opening fire, the Clinton camp broke its policy of generally not discussing the Secret Service dispute because, it has insisted, it has left the matter entirely in the hands of the agency and the Justice and Treasury departments, which so far have lost two court fights to block agents from having to testify.

But Clinton strategists concluded it was an opportune moment to speak out, reasoning that Starr overreached by issuing new subpoenas even as the matter was still pending at the U.S. Court of Appeals for the D.C. Circuit. In particular, they characterized Starr as excessive for targeting the one agent most responsible for ensuring the president's safety.

What Starr wants with Cockell remained unclear. As the head of the detail, Cockell, 47, is virtually the president's alter ego, constantly at his hip no matter where he goes and within easy earshot of many of Clinton's conversations. Yet Cockell did not begin working at the White House until the summer of 1996, after Lewinsky had already been transferred to the Pentagon, although as lead agent he may be privy to what other agents have seen and heard.

Some Clinton advisers said they feared Starr might try to ask Cockell about what he heard the president say after leaving the site of his Jan. 17 deposition in the Paula Jones case, where he was questioned at length about his relationship with Lewinsky. Cockell was in the limousine during the brief trip back to the White House along with Clinton and his private attorney, Robert S. Bennett.

There was no indication from Starr's office that he intends to question Cockell about the car ride and risk a separate court fight, but Bennett and Clinton's other attorney, David E. Kendall, suggested that was the obvious intent and would be an improper breach of attorney-client privilege.

"Let us be clear," they said in a joint statement. "Any backdoor attempt by this prosecutor to invade the president's right to consult with personal counsel will be aggressively and firmly resisted."

Cockell has hired a private attorney and may be advised not to appear today if a higher court does not step in, sources familiar with the deliberations said. The attorney would file a motion to quash or delay the subpoena, noting that it had just been delivered two days earlier and Cockell needed time to find and consult a lawyer.

If no court intervenes and officers do not appear or refuse to answer some questions under oath, Starr could seek to hold them in contempt.

A lawyer for two of the uniformed officers filed a motion yesterday asking Johnson to order that any testimony they give remain sealed and not provided to Congress in any impeachment report filed by Starr. Johnson did not rule on that request, but may today.

In case Secret Service officers do not testify, Linda R. Tripp, the onetime Lewinsky friend who taped her talking about having an affair with Clinton, has been told to return to the courthouse today for a possible sixth day before the grand jury.

In a related proceeding examining whether the Clinton administration tried to smear Tripp, Starr brought chief Pentagon spokesman Kenneth H. Bacon before a separate Alexandria grand jury yesterday to testify about the release of information from Tripp's security form to the New Yorker magazine. "I answered all their questions," Bacon said last night. "It was over in less than two hours and I think it's through."

By employing more aggressive tactics in the Secret Service battle, Starr is trying to speed up resolution of the court fight. The question of whether the latest subpoenas should be blocked could go to the Supreme Court right away, forcing the justices to signal whether they may eventually take the broader case of whether the Secret Service can assert a "protective function privilege."

If the Supreme Court declined to issue a stay, it would suggest that the justices are unlikely to review the case down the road, allowing Starr to proceed with questioning agents, according to lawyers familiar with the issues.

The more adversarial approach by Starr has alienated Justice Department officials, who until last week had nurtured what they considered an amicable working relationship with the independent counsel, even as they sparred in court.

In recent days, some senior department officials have concluded that Starr no longer feels any incentive to negotiate because of last week's unanimous ruling by a three-judge appeals panel rejecting the Secret Service's request to withhold testimony. With the strong legal hand, Starr appears intent on collecting all the information he can from the Secret Service without deferring to its concerns for security, administration officials said.

But some Starr defenders suggested that the Justice Department brought this situation on itself by persisting with an appeal to the full appellate court this week.

During a hearing on Capitol Hill, Senate Judiciary Committee Chairman Orrin G. Hatch (R-Utah) said he was "extremely dismayed" that the department appealed what he called an "eminently reasonable" court ruling. "The decision to appeal at this time calls into serious question the real motivations of both the Department of Justice and the Secret Service," Hatch said.

Attorney General Janet Reno, appearing before the committee, maintained that the issue was the president's safety, not his legal defense. "Let me assure you, this is not done for delay," she said. "It's a difficult issue."